1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for processing semiconductor substrates. More specifically, to a method and apparatus for thermally treating semiconductor substrates.
2. Description of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors, and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is ion implantation.
Ion implantation is particularly important in forming transistor structures on semiconductor substrates and may be repeated many times during chip fabrication. During ion implantation, a semiconductor substrate, typically comprising a silicon material and/or a silicon containing film, is bombarded by a beam of electrically charged ions, commonly called dopants. Ion implantation changes the properties of the material in which the dopants are implanted in order to achieve a particular level of electrical performance. Dopant concentration may be determined by controlling the number of ions in a beam of energy projected on the substrate and the number of times the substrate passes through the beam. The dopants are accelerated to an energy level that will enable the dopants to penetrate the silicon material or implant into the film at a desired depth. The energy level of the beam typically determines the depth at which the dopants are placed.
During ion implantation, the implanted film may develop a high level of internal stress. In order to relieve the stress and further control the resulting properties of the implanted film, the film is typically subjected to a thermal process, such as annealing. Post-ion implantation annealing is typically performed in a rapid thermal processing (RTP) chamber that subjects the substrate to a very brief, yet highly controlled thermal cycle that can heat the substrate from room temperature to approximately 450° C. to about 1400° C. RTP typically minimizes or relieves the stress induced during implantation and can be used to further modify film properties, such as changing the electrical characteristics of the film by controlling dopant diffusion.
The RTP heating regime generally includes heating from a radiant heat source, such as lamps and/or resistive heating elements. In a conventional RTP system, the substrate is heated to a desired temperature, and then the radiant heat source is turned off, which causes the substrate to cool. In some systems, a gas may be flowed onto the substrate to enhance cooling. However, as processing parameters continue to evolve, temperature ramp up and heating uniformity during RTP requires closer monitoring and control. While conventional RTP chambers rely on the radiant heat source to rapidly heat the substrate to a desired temperature, the challenges arise when the substrate requires cooling to improve heating uniformity, and/or when the substrate needs to be rapidly cooled. For example, if a significant temperature gradient exists across the substrate, the substrate may plastically deform or warp, which may be detrimental to subsequent processes performed on the substrate. Further, the faster cooling and/or enhanced temperature control of the substrate may result in higher throughput and enhanced dopant uniformity.
Therefore, what is needed is an apparatus and method for rapid heating and cooling of a semiconductor substrate, with enhanced control of heat uniformity.